1. Field of the Invention
This invention relates to an apparatus for forming a wrapping web into a tubular configuration. More particularly, it relates to a former for use in a form-fill-packaging machine of the type in which a web of wrapping material is formed into a wrapping tube to entube articles, the resulting tube of wrapping material being filled with articles and subsequently sealed intermediate the entubed articles. This invention is concerned with an improvement on such a former by means of which the diameter of the opening of formed wrapping tubes may be steplessly adjusted; and with an improved actuating mechanism adapted to adjustably advance and retract an elastic sheet material constituting the former.
2. Description of the Prior Art
Web forming devices or formers are usually used in vertical packaging machines, horizontal packaging machines and all the other form-fill-sealing machines of the type in which a wrapping web is formed into a tubular body which is to be filled with articles and sealed on three or four of its sides so as to entube the articles. Thus, the formers are utilized to form a wrapping web fed from the parent roll into a tubular body, and various types of formers have hitherto been proposed to form such a wrapping tube. In general, previously known formers are of the fixed type in which the diameter of the formed tubular body cannot be varied. When it is desired to change the diameter of packages, therfore, a suitably sized former is selected from variously sized formers prepared beforehand, to conform to the desired size of the wrapping tube to be formed. It is to be noted, however, that an extremely intricate operation is required to replace the former, and the machine operation has to be interrupted for replacing the former, thereby decreasing the operating efficiency.
Thus, in view of the requirement that dimensions of tubular packages be altered depending upon the various factors such as the shape, size and volume of the objects to be wrapped, several web forming devices have hitherto been proposed which permit production of tubular packages having changing diameters by variably adjusting the width of the tubular web. For instance, Japanese Utility Model Publication No. 53-50697 discloses a technical conception wherein the machine body includes an extension having an opening and adapted to carry a pair of web forming devices each having an L-shaped fixture. The backside gap between the web forming devices is adjusted by loosening and moving tightening screws of the L-shaped fixtures, to thereby obtain a desired width of the wrapping tube to be formed. In this prior art device, however, the range of adjustment in the opening width is narrow and yet the arrangement is complicated and the operation is troublesome. Thus, it is practically difficult to produce tubular packages of arbitrary sizes by such a device.
Japanese Laid-Open Utility Model Publication No. 55-66906 discloses a former which comprises a combination of two semi-tubular divided bodies, the spacing between the bodies being adjustable by means of bolts and nuts. In this arrangement, however, the chute serving as a forming tube is inserted within the former and yet the size of the outer periphery of the chute is fixed. Apparently, the range of adjustment of the wrapping tube diameter is extremely limited as with the device illustrated in Publication No. 53-50697.
Another disadvantage found in the prior art devices is that the gap adjusting mechanism used therfor is relatively complex in construction and yet gaps cannot be arbitrarily determined for various sizes of wrapping tubes.